The human foot is a highly complex and exceedingly strong anatomical structure which is typically able to absorb and distribute high impact forces in a flexible and resilient manner. The human foot and associated ankle include 52 bones and 33 joints. In addition, the foot includes a complex system of muscles that all act upon the toes, and which may be grouped as abductors, adductors, flexors, or extensors. Tendons connect muscles to the bones and are guided and contained between the lower leg and the foot by portions of the fascia located in front of and behind the ankle. The foot includes vascular, connective, adipose, cartilaginous, ligamentous, and nervous tissues. A majority of these components have a general longitudinal orientation relative to the foot. In combination, these components operate in concert to provide the body with support, balance, and mobility. Damage or failure of any one of these components can seriously impair the quality of life of an individual.
Anatomically, the weight of the body in the erect posture is supported by a group of arches formed by the tarsal and metatarsal bones of the foot. The bones forming these arches are connected and reinforced by ligaments and tendons. The predominant arches are the antero-posterior arches, which include the medial and lateral arches. The medial arch is formed by bones which include the calcaneus, the talus, the navicular, the three cuneiforms, and the first, second, and third metatarsals. The apex of the medial arch occurs approximately at the superior articular surface of the talus and the two ends of the arch include the tuberosity on the plantar surface of the calcaneus posteriorly, and the heads of the first, second, and third metatarsal bones anteriorly. The medial arch is reinforced by plantar fascia, plantar ligaments, and intrinsic foot muscles and functions to provide medial stability to the entire foot.
The second antero-posterior arch is the lateral arch, which includes the calcaneus, the cuboid, and the fourth and fifth metatarsals. The apex of the lateral arch occurs approximately at the talocalcaneal articulation and is much less distinct than medial arch. Generally, the lateral arch does not bear as much weight as medial arch and is reinforced by plantar fascia, plantar ligaments, and intrinsic foot muscles.
In the past several decades, athletic endeavors associated with running have been identified with injuries to the lower extremities. Running has been recognized to place enormous stresses on the feet and lower legs. It is often cited that during a typical 5K run, a runner's feet will impact the ground about 3000 times with a force equivalent to about 2-3 times the body weight of the runner. This repetition and force can result in acute and chronic injury. Primarily the injury is attributed to overuse, and many attempts have been made to identify commonalties related to the configuration of the foot that act as a trigger for these injuries. For example, runners with excessively high, cavus, or low, planus, foot arch structures are thought to suffer a higher instance of various lower extremity and foot injuries than runners with moderate or normal foot arch structure. These injuries include: tibial stress syndrome; patellofemoral pain syndrome; posterior tibialis tendinitis; lateral ankle sprains; and/or general knee pain. In addition, overuse injuries are attributable to excessive eversion of the foot being translated into excessive tibial rotation which occurs because of excessive motion at the subtalar joint.
Abnormalities associated with disease conditions, for example, severe rheumatoid arthritis also appear to create gait abnormalities that result in repeated, excessive plantar pressures. Rheumatoid arthritis frequently leads to foot and ankle deformities that ultimately modify the foot strike pattern of the afflicted individual through such things as a greater pronation angle and increased pronation velocity.
Furthermore, normal biomechanical functioning of the foot and ankle complex as well as biomechanical structural changes often occur following trauma to the foot. For example, ankle fractures, calcaneal fractures, subtalar joint dislocations, and/or tarsometatarsal joint dislocations can lead to recurring pain in the lower leg and foot due these biomechanical changes. Such conditions as plantar fasciitis, an inflammation of the heel of the foot, can result from trauma to the plantar fascia of the foot, which in turn can lead to the development of pathologic changes to the patient's gait cycle.
Prevention of the above discussed tissue damage or failure and/or the amelioration or elimination of symptoms associated with damaged or failed tissues have been attempted through the use of conventional orthosis devices. Conventionally, orthoses are devices designed to stabilize or immobilize a portion of the body, prevent deformity, prevent injury and/or provide functional assistance. For example, an orthosis can be associated with the foot so as to protect bone and soft tissue, correct improper tissue alignment, to cushion bones exposed by tissue atrophy, and/or to protect skin from damage due to, for example, neuropathic anesthesia. Typically the term “foot orthoses” is used to reference devices that are placed into shoes. Conventionally foot orthoses have become standard for the treatment of injuries of the foot, ankle, and lower extremity. From a biomechanical perspective, they offer a means of resolving symptoms by placing the foot and the lower extremity in a more advantageous position, thus altering applied tissue stresses. Orthoses have been widely used as part of treatment programs for foot and ankle injuries in sports.
Conventionally, effective orthosis fabrication requires custom fitting on an individual patient basis. This fabrication is typically initiated by first determining the neutral position of the patient's foot and then creating a cast of this neutral position. This time and labor intensive custom fitting is thought to be the best way of reducing abnormal structural pressures, reducing formation of calluses and ulcers, and/or protecting the foot from external trauma. However, in addition to the time and labor requirements, the typical custom fit orthosis does not adequately account for the longitudinal orientation of the muscles, tendons, and ligaments extending between portions of the human foot. The conventional foot orthosis, in contrast, is typically designed longitudinally along the same direction of the muscle, tendon and ligament groups of the arch that are affected by the impact of a foot strike. Furthermore, they commonly require specialized and costly fitting to accommodate various sized human feet as well as adding substantial weight to the foot hardware.